This application is based on application No. JP 2000-125703 filed in Japan, the contents of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an improved light shutter device, and more particularly, to an improved light shutter device driving method Specifically, it relates to a light shutter device driving method, and more particularly, to a light shutter device that comprises multiple light shutter elements located on a substrate made of a material having an electro-optical effect, wherein the ON/OFF control of light is carried out through the action on each light shutter element of an electrical field generated from a pair of electrodes, as well as to a driving method for such light shutter device.
2. Description of the Related Art
Various light shutter devices are provided that comprise light shutter substrates made of PLZT, a material that has an electro-optical effect, in an array and in which light is turned ON/OFF on an individual pixel basis in order to form an image on photographic paper or film using a silver halide material or on an electronic photosensitive medium.
A specific principle is shown in FIG. 9. When no voltage is applied to the pair of electrodes 14 and 15 located on the light shutter chip 12, the incident light is blocked by the polarizer 5 located in front of the light shutter chip and the analyzer 7 located on the light exit side, and therefore such light does not exit from the chip. When a voltage is applied to the electrodes 14 and 15, double refraction occurs in the light that enters the PLZT. The light that enters the light transmitting area (light shutter element) 13 through the polarizer 5 is polarized 90 degrees by the light shutter chip 12 such that the light passes through the analyzer 7. Through this operation, the light shutter device turns ON/OFF.
One example of the electrode construction on the conventional light shutter chip 12 is shown in FIG. 10. In this chip 12, light shutter elements 13 (13a, 13b . . . ) are alternately located on the lines X, X that divide the one line image data into two, a common electrode 14, which is connected to ground and is formed therebetween, and individual electrodes 15 (15a, 15b . . . ), to each of which a prescribed voltage is individually applied and which are formed such that the light shutter elements 13 are situated between the individual electrodes 15.
In each light shutter element, the largest amount of pass-through light may be obtained when the incident light is polarized by 90 degrees. The voltage applied to cause this polarization is called half-wavelength voltage. Therefore, driving of this type of light shutter element is carried out using the half-wavelength voltage with which the pass-through light amount is maximized, but a phenomenon occurs in which the half-wavelength voltage and pass-through light amount fluctuate due to the effect of the electrical fields that extend from the adjacent elements (in this specification, this phenomenon is called cross-talk).
For example, to focus on one element 13e in FIG. 10, the lit state (i.e., the amount of pass-through light) of the element 13e should be determined based on the voltage (electrical field) applied to the individual electrode 15e and the common electrode 14. However, when the elements 13c and 13g that are adjacent to the element 13e on the line X are also lit, the electrical fields from the individual electrodes 15c and 15g also extend to the element 13e. Consequently, the half-wavelength voltage by which to drive the element 13e and the amount of pass-through light passing therethrough undergo changes depending on the ON/OFF state of the adjacent elements 13c and 13g. 
Such cross-talk does not ordinarily take place between elements that face each other across the common electrode 14, because the common electrode 14 operates as an electrical field barrier. However, where the common electrode 14 is narrow, it is possible for the electrical fields from the individual electrodes 15d and 15f that face the element 13e across the common electrode 14 to extend to the element 13e, causing a cross-talk phenomenon.
FIG. 11 shows the relationship between the voltage applied to the target element 13e and the amount of pass-through light passing therethrough. FIG. 12 shows the waveforms of the voltages applied to the elements 13c, 13e and 13g, respectively, and the photoresponse waveform of the element 13e for each one line image draw cycle.
Characteristic A shown in FIG. 11 indicates the case in which both the adjacent elements 13c and 13g, as well as the element 13e, are simultaneously turned ON, and corresponds to the first cycle in FIG. 12. Characteristic B indicates the case in which either adjacent element 13c or 13g is turned ON, and corresponds to the second or third cycle in FIG. 12. Characteristic C indicates the case in which both adjacent elements 13c and 13g are turned OFF, and corresponds to the fourth cycle in FIG. 12.
As is clear from these characteristics A, B and C, the half-wavelength voltage and the pass-through light amount of the element 13e change depending on the states of operation of the adjacent elements 13c and 13g. For example, where the element 13e is driven using the half-wavelength voltage (approximately 142V) when the elements 13c and 13g are simultaneously turned ON, if either element 13c or 13g is OFF, the element 13e pass-through light amount is reduced by approximately 5%, and if both of the elements 13c and 13g are OFF, the element 13e pass-through light amount is reduced by approximately 16%.
The present invention was made in view of these circumstances, and an object hereof is to provide an improved light shutter device. Another object of the present invention is to provide an improved light shutter device driving method. More specifically, an object of the present invention is to provide a light shutter device and driving method therefor in which the cross-talk phenomenon in which the light shutter elements affect each other may be effectively prevented and the amount of pass-through light of each light shutter element is stabilized.
In order to attain these and other objects, one aspect of the present invention is a driving method for a light shutter device comprising multiple light shutter elements located on a substrate made of a material having an electro-optical effect, wherein light is controlled to turn ON/OFF through the action of an electrical field generated from a pair of electrodes on each light shutter element, and wherein an electrical field does not operate essentially simultaneously on light shutter elements as to which the cross-talk phenomenon occurs in their respective electrical fields.
In the driving method pertaining to the above aspect, an electrical field does not operate essentially simultaneously on light shutter elements that experience a mutual cross-talk effect. Therefore, each light shutter element can obtain a constant amount of pass-through light at all times based on the application of a constant voltage to the electrodes, resulting in the formation of high-quality images.
The concept that xe2x80x98an electrical field does not operate essentially simultaneouslyxe2x80x99 includes the case in which the effect of cross-talk does not appear in the image as a practical matter even if the electrical fields of the elements overlap slightly, as well as the case in which the actions of each electrical field on each light shutter element are completely separate from each other.
In order to perform driving while ensuring that each electrical field does not affect more than one element at the same time, it is preferred from the viewpoint of simplified driving that one line cycle be divided into at least two periods and that the light shutter elements that experience mutual cross-talk be alternately turned ON in each period. If light shutter elements that are arranged at a 1/2 line pitch difference are alternately turned ON in each of the two periods of one line cycle, the cross-talk phenomenon, as well as minute discrepancies in one line image, may be eliminated through simplified driving.
In addition, it is also acceptable if a large number of pulses are supplied per line cycle and if each pulse is allocated such that adjacent elements are not turned ON at the same time. Although this method entails a higher drive frequency, it allows cross-talk and minute discrepancies in one line image to be eliminated.